1. Field of the Invention
The present invention generally relates to a power converting mechanism in an electric actuator for converting rotary power into linear power, and more particularly, to a power converting mechanism in an automobile door lock device suitable for use when the rotary power of a remote-controlled motor is converted into linear power of a part to be driven (output member), thereby to automatically drive a door-lock member coupled to the driven part.
2. Description of the Prior Art
The power conversion has conventionally been carried out by employing a link or a rack-and-pinion, etc., that is, the link converting mechanism or the rack-and-pinion converting mechanism has been conventionally used for the power conversion. In the aforementioned link conversion mechanism, the relationship of the thrust (F), the input torque (T), the pitch of a link arm (L), the stroke (S) and the rocking angle (.theta.) of the link arm is represented by equations F=T/L and S=2 sin .theta.. Therefore, the stroke is 2L at the largest, and a large stroke can be obtained only at the sacrifice of the thrust. On the other hand, in the case of the rack-and-pinion converting mechanism, the relationship of the pitch radius (r) of a pinion, the thrust (F) and the input torque (T) is represented by an equation F=T/r, resulting in limit of the reduction of speed in relation to the minimum number of teeth of the gear.
Meanwhile, for solving the above-described disadvantages in the prior art and for determining the stroke and the scale of reduction in speed freely to some extent, the use of a gear and a screw for the power conversion is proposed in Japanese Patent Laid-open Publication Tokkaisho No. 61-261587 (261587/1986).
The above gear-and-screw mechanism is of such construction that a screw 1 (a rotating shaft provided in an external thread) is interlocked with the rotation of a motor 2 through gears 3 and 4, thereby to linearly move an output member 5 screwed in the screw 1. Moreover, an output rod 6 connected to a driver lever to be operated is detachably engaged with the output member 5 by a clutch member 8 provided with a spring 7. Therefore, the above-described gear-and-screw mechanism is considerably complicated in the construction, with an increased number of parts required, resulting in high manufacturing cost and many assembling troubles.